Fix lldb-vscode frame test failure

Previous patch (https://reviews.llvm.org/D126013) added a new "optimized"
attribute to DAP stack frame this caused some tests, like
lldb-vscode/coreFile/TestVSCode_coreFile.py
to fail because the tests explicitly check for all attributes.

To fix the test failure I decided to remove this attribute.

Differential Revision: https://reviews.llvm.org/D126225